Method and apparatus for adjusting color edge center in color transient improvement

Abstract

An improved method for color transient enhancement in an input video frame of pixels. The luminance value of a current pixel is compared to that of neighboring pixels. A correction value is determined and the chrominance value of the current pixel is “pushed” towards the neighboring pixel that has a luminance value closest to that of the current pixel, by adding the correction value to the current pixel's chrominance value. The original video frame is also separately processed using a CTI method, and the current pixel's corrected chrominance value is combined with the corresponding pixel in the output of the CTI processing by soft switching unit to generate an output video frame that is an enhanced version of the input video frame.

1. A method of processing an input frame of pixels representing a video signal having a transient response, each pixel having a luminance value and a chrominance value, comprising the steps of:
 enhancing color transition by adjusting the chrominance value of a color edge center based on the luminance values of neighboring pixels to provide enhanced pixels. 
 
     
     
       2. The method of  claim 1 , wherein adjusting the chrominance value of a selected pixel further includes the steps of:
 comparing the luminance value of the selected pixel with luminance values of the neighboring pixels, to identify a pixel among the neighboring pixels with a luminance value closest to the luminance value of the selected pixel; and 
 modifying the chrominance value of the selected pixel to bring the chrominance value of the selected pixel closer to the chrominance value of the identified neighboring pixel. 
 
     
     
       3. The method of  claim 2 , wherein modifying the chrominance value of the selected pixel to bring the chrominance value of the selected pixel closer to the chrominance value of the identified neighboring pixel further includes the steps of:
 determining a correction value based on the chrominance and luminance values of the identified pixel; and 
 adding the correction value to the chrominance value of the selected pixel, to generate a corrected chrominance value for the selected pixel. 
 
     
     
       4. The method of  claim 3 , wherein:
 each chrominance value has a U component and a V component, 
 each correction value has a U component and a V component, and 
 adding the correction value to the chrominance value of the selected pixel further includes the steps of adding the correction value components to the respective chrominance value components of the selected pixel. 
 
     
     
       5. The method of  claim 4 , wherein:
 the U component of the correction value is g i (x)*dU i (x), and 
 the V component of the correction value is g i (x)*dV 1 (x), wherein:
 i denotes the identified neighboring pixel in the frame, 
 g i (x) is a gain control function based on a difference in between the luminance value of the selected pixel x and the luminance value of the identified pixel, 
 dU i (x) represents a difference between the U component of the chrominance value of the selected pixel x and the U component of the chrominance value of the identified pixel, and 
 dV i (x) represents a difference between the V component of the chrominance value of the selected pixel x and the V component of the chrominance value of the identified pixel. 
 
 
     
     
       6. The method of  claim 2 , wherein:
 the frame comprises an array of pixels arranged as rows and columns, and 
 adjusting the chrominance value of the selected pixel further includes the steps of:
 comparing the luminance value of the selected pixel with luminance values of the neighboring pixels in columns to the right and left and the selected pixel, to identify a pixel among those neighboring pixels with a luminance value closest to the luminance value of the selected pixel; and 
 modifying the chrominance value of the selected pixel to bring the chrominance value of the selected pixel closer to the chrominance value of the identified neighboring pixel. 
 
 
     
     
       7. The method of  claim 2 , wherein:
 the frame comprises an array of pixels arranged as rows and columns, and 
 adjusting the chrominance value of the selected pixel further includes the steps of:
 comparing the luminance value of the selected pixel with luminance values of the neighboring pixels in rows above and below the selected pixel, to identify a pixel among those neighboring pixels with a luminance value closest to the luminance value of the selected pixel; and 
 modifying the chrominance value of the selected pixel to bring the chrominance value of the selected pixel closer to the chrominance value of the identified neighboring pixel. 
 
 
     
     
       8. The method of  claim 2 , wherein modifying the chrominance value of the selected pixel further includes the steps of:
 comparing a difference between the luminance value of the selected pixel and the luminance value of the identified pixel with a threshold value; and 
 if the difference exceeds the threshold value, then modifying the chrominance value of the selected pixel to bring the chrominance value of the selected pixel closer the chrominance value of the identified neighboring pixel. 
 
     
     
       9. The method of  claim 2 , wherein modifying the chrominance value of the selected pixel further includes the steps of:
 comparing a difference between the chrominance value of the selected pixel and the chrominance value of the identified pixel with a threshold value; and 
 if the difference exceeds the threshold value, then modifying the chrominance value of the selected pixel to bring the chrominance value of the selected pixel closer the chrominance value of the identified neighboring pixel. 
 
     
     
       10. The method of  claim 2 , wherein modifying the chrominance value of the selected pixel further includes the steps of:
 comparing a first difference between the chrominance value of the selected pixel and the chrominance value of the identified pixel with a first threshold value; 
 comparing a second difference between the luminance value of the selected pixel and the luminance value of the identified pixel with a second threshold value; and 
 if the first difference exceeds the first threshold value, and if the second difference exceeds the second threshold value, then modifying the chrominance value of the selected pixel to bring the chrominance value of the selected pixel closer to the chrominance value of the identified neighboring pixel. 
 
     
     
       11. The method of  claim 1 , further comprising the steps of:
 performing color transition improvement (CTI) on the input pixels to provide pixels with improved color transitions; and 
 combining the values of said enhanced pixels and the pixels with improved color transitions, to generate an improved and enhanced frame of pixels. 
 
     
     
       12. The method of  claim 11 , wherein combining the values further includes the steps of:
 determining whether the color transition near the center of the color edge is below a predetermined value; and 
 if so, then providing the CTI results as the enhanced output; otherwise, providing the enhanced pixels as the enhanced output. 
 
     
     
       13. The method of  claim 11 , wherein combining the values further includes the steps of:
 determining a second derivative of the color edge transition; and 
 if the second derivative is essentially non-zero, then providing the CTI results as the enhanced output; otherwise, providing the enhanced pixels as the enhanced output. 
 
     
     
       14. An apparatus for processing an input frame of pixels representing a video signal having a transient response, each pixel having a luminance value and a chrominance value, comprising:
 a correction value generator for generating a correction value for adjusting a selected pixel's color edge center based on luminance values of neighboring pixels; and 
 a combiner for adding the correction value to the chrominance value of the selected pixel to provide enhanced pixels. 
 
     
     
       15. The apparatus of  claim 14 , wherein:
 the correction value generator further comprises a control unit that compares the luminance value of the selected pixel with luminance values of the neighboring pixels, to identify a pixel among the neighboring pixels with a luminance value closest to the luminance value of the selected pixel, and determines the correction value based on the luminance value of the identified pixel, and 
 the combiner modifies the chrominance value of the selected pixel by adding the correction value to the chrominance value of the selected pixel to bring the chrominance value of the selected pixel closer the chrominance value of the identified neighboring pixel. 
 
     
     
       16. The apparatus of  claim 15 , wherein:
 each chrominance value has a U component and a V component, 
 each correction value has a U component and a V component, and 
 the combiner adds the correction value components to the respective chrominance value components of the selected pixel. 
 
     
     
       17. The apparatus of  claim 16 , wherein the control unit generates the U component of the correction value as g i (x)*dU i (x), and generates the V component of the correction value as g i (x)*dV i (x), wherein
 i denotes the identified neighboring pixel in the frame, 
 g i (x) is a gain control function based on a difference between the luminance value of the selected pixel x and the luminance value of the identified pixel, 
 dU i (x) represents a difference between the U component of the chrominance value of the selected pixel x and the U component of the chrominance value of the identified pixel, and 
 dV i (x) represents a difference between the V component of the chrominance value of the selected pixel x and the V component of the chrominance value of the identified pixel. 
 
     
     
       18. The apparatus of  claim 15 , wherein the control unit is further configured to compare a difference between the luminance value of the selected pixel and the luminance value of the identified pixel with a threshold value, and if the difference exceeds the threshold value, then generates said correction value. 
     
     
       19. The apparatus of  claim 15 , wherein the control unit is further configured to compare a difference between the chrominance value of the selected pixel and the chrominance value of the identified pixel with a threshold value, and if the difference exceeds the threshold value, then generate the correction value. 
     
     
       20. The apparatus of  claim 15 , wherein the control unit is further configured to
 (i) compare a first difference between the chrominance value of the selected pixel and the chrominance value of the identified pixel with a first threshold value, 
 (ii) compare a second difference between the luminance value of the selected pixel and the luminance value of the identified pixel with a second threshold value, and 
 (iii) if the first difference exceeds the first threshold value, and if the second difference exceeds the second threshold value, then generate the correction value. 
 
     
     
       21. The apparatus of  claim 14 , further comprising:
 a color transition improvement (CTI) unit that processes the input pixels to provide pixels with improved color transitions; and 
 a switch that combines the values of said enhanced pixels and the pixels with improved color transitions, to generate an improved and enhanced frame of pixels. 
 
     
     
       22. The apparatus of  claim 21 , wherein:
 the switch is further configured to determine whether the color transition near the center of the color edge is below a predetermined value, and if so, then provides the CTI results as the enhanced output; otherwise, provides the enhanced pixels as the enhanced output. 
 
     
     
       23. The apparatus of  claim 21 , further comprising a differentiator that determines a second derivative of the color edge transition, and the switch is further configured to determine whether the second derivative is essentially non-zero, and if so, provides the CTI results as the enhanced output; otherwise, provides the enhanced pixels as the enhanced output.